Sealed Batteries: Are They Really Sealed?

New batteries are advertised as sealed. So why do they need venting?

Question: The batteries on my boat are show below. The Lifelines are known as sealed batteries. So, since my batteries are sealed, do I have to worry about ventilating the compartment the batteries are stored in, like I did with my old batteries?

Sealed batteries like these Lifelines can still off-gas if they are overcharged.

Answer: Yes you do. It is important to remember that although these newer battery types and designs are much less prone to “gassing” as they are being recharged, any battery can gas if it is overcharged due to a faulty voltage regulator or an improperly calibrated shore power charger.

Your batteries are more properly known as “VRLA” batteries, or Valve Regulated Lead Acid. The battery has a small check valve built into its top that is designed to open and vent when the battery’s internal pressure reaches 1-3 PSI, depending upon the vendor. This will then allow for the release of hydrogen gas from inside the battery. Since hydrogen is highly explosive, neither the USCG nor ABYC give “sealed” batteries any special breaks as to where they get installed.

The good news? Hydrogen is lighter than air so it rises. It also mixes with air quite readily; a quite small opening (about 12mm or half an inch in the upper-most covering for the compartment shown) would be sufficient to ventilate the area in the event of a leak.